Technical Field
The present invention relates to a radio communication apparatus and a radio communication method.
Description of the Related Art
In 3rd Generation Partnership Project Long-term Evolution (3GPP LTE), in the case where a data channel (physical uplink shared channel (PUSCH)) and a control channel (physical uplink control channel (PUCCH)) are transmitted in the same subframe, a mobile station multiplexes the two channels by time division multiplexing (TDM), as shown in FIG. 1. That is, data is punctured by control information such as an ACK or a NACK. By TDM multiplexing, it is possible to maintain single carrier characteristics and prevent increase of cubic metric (CM). On the other hand, because data is punctured, there is a problem that data reception performance deteriorates.
In an uplink channel of LTE-Advanced, which is an evolved version of 3GPP LTE, in the case where a PUSCH and a PUCCH are transmitted in the same subframe, a mobile station is expected to multiplex the two channels by frequency division multiplexing (FDM), as shown in FIG. 2. A mobile station transmits a PUSCH and a PUCCH at the same time by mapping the PUSCH and the PUCCH in different frequency bands. Because data is not punctured by FDM multiplexing, it is possible to prevent deterioration of reception performance. On the other hand, there is a problem that single carrier characteristics are not maintained and multicarrier transmission is performed, so that CM increases. When CM increases, the maximum transmission power that can be transmitted by a mobile station lowers, so that power head room (hereinafter referred to as “power head room (PHR)”) of a mobile station located, for example, at the cell edge, becomes small, and it becomes not possible to set the transmission power required by a base station, lowering the reception performance of the base station significantly. PHR refers to the margin of transmission power of a mobile station or transmission power of a mobile station that can be increased.
A method of multiplexing a PUSCH and a PUCCH at a mobile station, that is, a method in which a base station controls whether to perform multiplexing by TDM (hereinafter referred to as “TDM transmission mode”) or perform multiplexing by FDM (hereinafter referred to as “FDM transmission mode”) based on the PHR of a mobile station, is under consideration (for example, see Non-Patent Literature 1). Specifically, in the case where the PHR of a mobile station is large (that is, the margin of transmission power is large), a base station applies the FDM transmission mode, which does not subject to the influence of increase of CM, so as to prevent deterioration of PUSCH reception performance. Further, in the case where the PHR of a mobile station is small (that is, the margin of transmission power is small), a base station applies the TDM transmission mode, so as to prevent increase of CM and prevent deterioration of PUSCH reception performance.
Non-Patent Literature 1 discloses that, in the case of applying the FDM transmission mode, it is necessary to preferentially ensure transmission power of a PUCCH, for which retransmission control processing is not performed so as to require higher quality, compared to a PUSCH. That is, in the FDM transmission mode, when setting the ratio of transmission power of a PUSCH to a PUCCH, transmission power of the PUCCH is ensured first, and transmission power of a PUSCH is set within the range of the remaining transmission power. By this means, it is possible to prevent deterioration of performance of a PUCCH, which requires higher quality.
Here, the definitions and methods of reporting of PHRs used in LTE will be described below. In LTE, as shown in FIG. 3, only PHR that is determined based on transmission power of a PUSCH as a reference, is defined. In LTE, a base station uses PHR to control the transmission bandwidth and the modulation and channel coding scheme (MCS) of a PUSCH of a mobile station. A base station can receive a PUSCH with a reception quality desired by the base station, by controlling the transmission bandwidth and MCS of a PUSCH of a mobile station so that transmission power of a PUSCH to be transmitted by a mobile station does not exceed the maximum transmission power of the mobile station.
Non-Patent Literature 2 discloses the definition of PHR and the transmission condition of PHR by equation 1.PHR_pusch=Pmax−Ppusch  (Equation 1)
In equation 1, PHR_pusch is PHR [dB] based on a PUSCH, and Pmax is the maximum transmission power [dBm] of a mobile station. Ppusch of equation 1 is transmission power of a PUSCH and is defined by following equation 2.Ppusch=10 log10M+P0+α·PL+ΔMCS+f(Δi)  (Equation 2)
In equation 2, M is the number of frequency resource blocks to be assigned, P0 is a value [dBm] set from a base station, PL is a path loss level [dB] measured by a mobile station, α is a weighted coefficient to show the compensation rate of path loss, ΔMCS is an offset depending on the MCS, and f(Δi) is a transmission power control value for which closed loop control is performed (for example, relative values of +3 dB or −1 dB) and is the result of addition including the past transmission power control value.
P0, α, and ΔMCS are parameters to be reported from a base station to a mobile station, and are values that are known by a base station. On the other hand, PL and f(Δi) are values that cannot be known correctly by a base station. Although f(Δi) is a parameter to be reported from a base station to a mobile station, there is a case where a mobile station cannot receive that command (cannot detect a control channel (PDCCH)). Because a base station cannot determine whether or not a mobile station can correctly receive a command, once a mobile station fails to receive a transmission power control value from a base station, a discrepancy of recognition between the mobile station and the base station occurs. As described above, because a base station cannot know PHR of a mobile station correctly, PHR needs to be reported from a mobile station.
PHR is reported from a mobile station in a cycle determined by a base station in advance. PHR is reported as medium access control (MAC) information of transmission data by a PUSCH using six bits.